I think the reason this debate keeps happening is that there is not an agreed upon definition of what terms like "good" and "evil" mean, or how to measure them. So positing that alignment is a real force doesn't give us much to go on.
No, it doesn't. But, I refer back to the question in the OP - "What justifies a position of
muscular neutrality?"
The metaphysics of how it all actually works
isn't specified in the game. As far as I am aware, Gygax himself never told us what happens if Good or Evil finally won. So, this answer has to be generated for any campaign in which it has, or might, happen. Most of us don't play games that will decide the Ultimate Question, so as GMs we never have to consider it.
But we can take that to mean that the characters within the fictional universe don't know for certain themselves. That leaves a lot of room for justification. If you don't really know the consequences, that can justify taking a muscular neutral stance. Or, if you believe that one side or the other will lead to a suffusion of energy in the prime material that will stop all natural processes, and you find those processes more dear than anything else, that might justify the stance.
Are these questions in the context of
@Umbran's premises? According to these premises, Good is totally ok with the destruction of the universe just to accomplish its goal of achieving the Ultimate Good.
For me, that's not Good. That's Evil with a hat.
Oh? What if the result is that, yes, the Prime Material as we know it ends, but all souls, past, present, and future wind up at peace in their appropriate paradise? Is that evil with a hat?
You cannot judge the moral position unless we lay out the full picture. But there is no one full picture for all game worlds and all tables. It is a campaign choice.
Also note that we are considering a universe that
does not care about our mortal opinions of Good and Evil. Mortals are
not the ones who decide what is, or isn't Good. Much like the family dog has opinions of what is good to eat - but, like, some dogs will ingest linoleum, charcoal briquettes, or basketballs. The dog can be wrong about what to eat. The mortal can be wrong about what is actually Good.